Biological phosphate transfer

Phosphate and vanadate complexes of zinc show a diversity of coordination behavior. Zn + accelerates polyphosphate hydrolysis (Section 9.3) appropriate zinc-organic phosphate complexes provide models for ATP transport and biological phosphate transfer, and are of possible relevance to DNA and RNA polymerases (see Zinc DNA-binding Proteins). 

The second type of biological electron transfer involves a variety of small molecules, both organic and inorganic. Examples of these are (a) nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP) as two electron carriers and (b) quinones and flavin mononucleotide (FMN), which may transfer one or two electrons. The structure of NAD and its reduced counterpart NADH are shown in Figure 1.12. 

The biological functions of the nucleic acids involve the participation of metal ions. In particular K+ and Mgr+ stabilize the active nucleic acid conformations. Mg2+ also activates enzymes which are involved in phosphate transfer reactions and in nucleotide transfer. The monomeric nucleotides are also involved in a number of metabolic processes and here again metal ions are implicated. Consequently, there has been considerable attention focussed on the coordination properties of these molecules as a means of understanding the mechanism of the metal ion involvements. A number of reviews are available which cover the studies on metal interactions.113 117... 

Examples include acetal hydrolysis, base-catalyzed aldol condensation, olefin hydroformylation catalyzed by phosphine-substituted cobalt hydrocarbonyls, phosphate transfer in biological systems, enzymatic transamination, adiponitrile synthesis via hydrocyanation, olefin hydrogenation with Wilkinson s catalyst, and osmium tetroxide-catalyzed asymmetric dihydroxylation of olefins. 

Kinases are enzymes that transfer a phosphate group from adenosine triphosphate (ATP), or other trinucleotide, to a number of biological substrates, such as sugars or proteins. They are part of a larger family of enzymes known as group transferases, but are limited to phosphate transfers. A typical reaction catalyzed by a kinase (e.g., hexokinase) is the phosphorylation of glucose upon its entry into a cell... 

Anomeric and double anomeric effects in phosphates The unusual stereoelectronic properties of negatively charged oxygen as a source of donor orbitals play a role in the formation of tetrahedral intermediates in nucleophilic addition/substitution at carbonyl. It also has important consequences for phosphate transfer reactions - one of the key types of chemical events in biology. 

The insensitivity of the ester dianion reaction to the nature of nucleophile can be used for trapping of unreactive nucleophiles in high energy bonds such as P-O-P in ATP. For these reactions, aU one needs to do is to stabilize the departing group This stabilization provides the key mechanistic insights into the key phosphate transfer in biology, the ATP synthase reaction. This reaction produces ATP in the human body from... 

Although it has been demonstrated that phosphonates can sometimes be incorporated to a limited extent in biological materials, in some cases the phosphonate appears to act as an inhibitor of phosphate transfer reactions. This is probably because of failure to interact with the appropriate phosphatase enzymes. 

Studies of hypervalent phosphorus compounds in biological phosphoryl transfer reactions include the preparation of novel anti-apicophilic penta-coordinated phosphoranes with frozen stereomutation using bulky biden-tate ligands. Kinetic studies have enabled the activation enthalpy of the stereomutation of an 0-equatorial phosphorane to its O-apical stereoisomer to be calculated. The involvement of hexacoordinated phosphoranes in phosphate transfer reactions has been clarified by theoretical calculations as well as in vitro studies. Applications of hexacoordinated compounds as catalysts have also been described. 

Estimate the values of the biological standard Gibbs energies of the following phosphate transfer reactions ... 

Douglas, K. T., 1976, A basis for biological phosphate and sulfate transfers-transition state properties of transfer substrates, in Progress in Bioorganic Chemistry, VoL 4 (E. T. Kaiser and F. J. Kezdy, eds.), p. 193, John Wiley Sons, New York. 

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